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Gil Cohen Magen/Reuters

A fallen tree on a car in hard-hit Queens did not faze a mobile user who apparently had cellphone service.

On Friday, four days after Hurricane Sandy, the major carriers — AT&T, Verizon Wireless, T-Mobile USA and Sprint — were still busily rebuilding their networks in the hardest-hit areas.

One-quarter of the cell towers in the storm zone were knocked out, according to the Federal Communications Commission. Many had no power, and their backup battery systems soon drained. The lines connecting those towers to the rest of the phone network were ripped out. Carriers deployed generators to provide power, but eventually those required more fuel — another limited resource.

In an emergency, a lack of cellphone reception can be dangerous, especially as more people have chosen to snip landlines out of their budgets. About 60 percent of American households have landlines, down from 78 percent four years ago, according to Chetan Sharma, an independent mobile analyst.

The carriers say they are trying their best to deal with an unusual disaster. But in the past, they have steadfastly objected to recommendations from regulators that they spend more money on robust emergency equipment, like longer-lasting backup batteries.

Neville Ray, chief technology officer of T-Mobile USA, said Hurricane Sandy was the biggest natural disaster he had ever dealt with and that service failures were inevitable.

“There’s an amount of preparation you can do, but depending on the size and scale and impact of the storm, it’s tough to anticipate every circumstance,” Mr. Ray said in an interview. “No degree of preparation can prevent some of those outages from happening.”

When networks fail, carriers deploy trucks, called C.O.W.’s, for cell on wheels, that act as temporary cell towers. But the companies say the challenge with deploying these trucks poststorm is connecting to power and to the wider phone network, which requires a microwave radio link to a working tower. Because of the density of the buildings in New York City, the trucks could serve only a small area, according to Mr. Ray.

The carriers have made other efforts to provide services while restoring their networks. AT&T wheeled out R.V.’s where customers could charge their phones. And it made an agreement to share networks with T-Mobile USA in the affected areas of New York and New Jersey. When customers of both companies place calls, they are carried by whichever network is available in the area.

But ultimately all of the carriers’ preparations and responses were not enough to get services running again in a hurry. Over the week the carriers reported gradual progress, and they declined to offer timelines indicating when customers could expect to have service again.

The unreliability of wireless networks may point to a bigger problem. Over the years, the phone companies have fought off regulators who want to treat them as utilities, arguing that if they are going to stay innovative, they cannot be burdened with the old rules that phone companies dealt with in the landline era. But as a consequence, there are almost no rules about what carriers have to do in an emergency, said Harold Feld, senior vice president for Public Knowledge, a nonprofit that focuses on information policy.

“With the new networks we’ve prized keeping costs down, we’ve prized flexibility and we’ve prized innovation,” said Mr. Feld, who wrote a blog post on Monday anticipating cell tower problems. “But we have not put stability as a value when we have been pushing to have these networks built out.”

Mr. Feld noted that after Hurricane Katrina in 2005, the F.C.C. recommended that carriers install backup batteries on their transmission towers that would last 24 hours, among other measures. But the carriers objected, presumably because they did not want to spend the money, he said. (Of course, 24 hours would not have been enough in many areas hit by the latest storm.)

In general, the carriers say it is in their own interest to fortify their networks for emergency situations, but Mr. Feld said this incentive was not enough.

“We ought to actually be doing this in the mind-set that there need to be actual rules, so that everybody knows how to behave when the crisis hits,” he said. “When I drive I have the best incentive in the world not to hit a telephone pole and not to slam into another car. But I still need speed limits, stop signs and stop lights.”

Debra Lewis, a spokeswoman for Verizon Wireless, said no amount of rules could have prepared carriers for the outcome of a storm like Hurricane Sandy.

“The fact is, regulation cannot anticipate the varied challenges that can arise in such situations, but we do learn from them and adapt accordingly to ensure we meet consumers’ needs,” Ms. Lewis said. She said the company prepared for natural disasters with generators and batteries that provided at least eight hours of power to cell sites.

Verizon Wireless said Friday evening that less than 3 percent of its network in the Northeast was still down. “In severely impacted areas, such as Lower Manhattan, while wireless service has yet to return to normal levels, coverage is good,” it said.

AT&T was the only major carrier that would not go into specifics about how much of its network was down. Anecdotally it seemed that in Manhattan at least, AT&T’s coverage was not as good as Verizon’s after the storm. One Twitter user directed this message at AT&T on Tuesday: “I live in lower manhattan. Vz has service u do not. You are ruining lives. I had to come midtown 2 call mom. Switching.”

Mark Siegel, a spokesman for AT&T, said the company would not comment because it was working on restoring its network.

A version of this article appeared in print on November 3, 2012, on page B6 of the New York edition with the headline: Cellphone Users Steaming at Hit-or-Miss Service.